One area of the body which is highly prone to chronic pain and degeneration of normal function is the hip joint. Whether caused by disease, aging, overuse, or injury, a portion of the population suffers from ailments relating to the hip. An often utilized solution to problems pertaining to the hip joint is total hip replacement (“THR”) surgery. Generally, THR surgery consists of the replacement of the existing ball and socket of the hip joint with prosthetic replacements. The head of the femur (i.e. —the ball) is typically removed and replaced with a femoral component made of biocompatible material, which mirrors the structure of the original bone. The acetabulum (i.e. —the socket) is typically reamed and fitted with a prosthetic acetabular cup component that corresponds and cooperates with the femoral component. This prosthetic acetabular cup component often times includes an outer shell constructed of a metallic material. Typically this shell is in the form of a hollowed out semi-sphere. An insert constructed of plastic, ceramic or metal received within the outer shell. In many cases, the acetabular cup component is anchored in the bone through the use of cement. Some cups are press fit in place. Still other cups are held in place by screws or fastening tabs integral with the cup itself. A combination of these fastening methods may be employed. Sometimes owing to the shape of the outer shell and/or the application of compound that enhance bone growth, the outer shell is designed to foster the growth of bone adjacent the shell. This new bone anchors the cup to the rest of the hip. Total hip replacement surgery has often proven successful in relieving many problems associated with the hip joint.
Even though total hip replacement surgery is often successful, it is sometimes necessary to perform the same surgery on the same hip. This may be necessary in situations in which wear or infection degrade the performance of the installed cup and femoral head. This sub-set of total hip replacement surgery is sometimes called revision surgery. In revision surgeries, it is necessary to remove the acetabular component previously implanted in the acetabulum. As mentioned above, these components may have been cemented in place or otherwise held by bone or fibrous tissue that may have grown in and around the component. Thus, their removal requires the cutting or chipping away of cement or bone material.
The Inventor's Assignee's U.S. Pat. No. 8,034,059, ACETABULAR SHELL REMOVAL INSTRUMENT, issued 11 Oct. 2011, the contents of which are explicitly incorporated herein by reference, discloses a surgical tool, acetabular cup remover, designed to perform a revision process. As its name implies, this tool is designed to remove an already implanted acetabular cup. This tool includes a head that is dimensioned to seat in and rotate in an implanted acetabular cup. Plural shafts extend away from this head. A blade is pivotally mounted to one of these shafts. The blade curves forward such that the blade curves around the head. One of the shafts is able to move longitudinally relative to the head. The blade is connected to this first shaft to pivot as a function of the longitudinal movement of the shaft. A second shaft is rigidly connected to the head. The blade is connected to this second shaft. Axial rotation of this second shaft results in a rotational movement of the blade around an arc. The second shaft is connected to a power tool that oscillates the shaft.
This tool is used by seating the head in the cup that is to be removed. The first shaft is pressed downwardly. This results in the pivoting of the blade against the bone in adjacent the cup. The power tool is actuated. Thus simultaneously the blade is pressed against bone and oscillated in an arc around the cup. The blade cuts the bone adjacent the cup. The tool is indexed and the blade pivoted so that the blade forms a cut that extend completely around the portion of the cup embedded in the bone. The formation of this cut separates the cup from the bone in which the cup is embedded. The cup can then be removed and a new one installed.
The above-described acetabular cup remover can be a useful tool for removing an acetabular cup. There is, however, an inefficiency associated with this tool. When the tool is used, the blade is typically oscillated around an arc that of 15° or less and more often 10° or less. Once one section of the cut is formed, the tool must be rotated so the blade can be positioned to cut an adjacent section of the cut. To form the cut it is necessary to rotate the power tool to which the cup remover is attached. This results in the centering of the blade over the portion of the bone in which the new section of the cut is to be formed. This requires the surgeon forming the cut to reposition how the power tool is held. Having to so reposition the tool may require the surgeon to hold the power tool in positions that, ergonomically, can impose a strain. Further, having to so reposition the handpiece can add to the time it takes to perform the revision surgical procedure. Having to perform these steps runs counter to one of the primary goals when performing surgery, that one should perform the procedure as quickly as possible to both minimize the likelihood the exposed tissue is open to infection and the amount of time the patient is held under anesthesia.